Addition-curable silicone adhesive compositions and N-heterocyclic silane adhesion promoters

ABSTRACT

Addition-curable platinum group metal catalyzed silicone compositions are provided which utilize an N-heterocyclic adhesion promoter, such as bis(trimethoxysilyltrimethylene) 2,6 pyridine dicarboxylate. Cohesive bonding is effected on both plastic and metal substrates at temperatures of less than 100° C. and in less than 1 hour.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to copending application Ser. No. 08/165,625, filedDec. 13, 1993, pending, filed concurrently herewith.

BACKGROUND OF THE INVENTION

The present invention relates to platinum group metal catalyzedaddition-curable silicone adhesive compositions employing anN-heterocyclic silane, such as bis(trimethoxysilyltrimethylene)2,6pyridine dicarboxylate, as an adhesion promoter.

As shown by Kasuya, U.S. Pat. No. 3,284,406, the adhesion of a curedplatinum catalyzed addition-curable silicone composition onto asubstrate is achieved by effecting the cure of the silicone compositionat a temperature such as 100° C. for at least one hour.

Mitchell et al, U.S. Pat. No. 5,164,461, which is incorporated herein byreference, is directed to the use of certain silylmaleates,silylmaleimides or silylfumarates, such asbis[3-(trimethoxysilyl)alkyl]fumarates as adhesion promoters inaddition-curable silicone adhesive compositions. Although theaddition-curable silicone compositions of Mitchell et al have been foundto be self-bonding to various substrates, such as plastics, metals orglass, these silicone adhesive compositions also require a temperatureof about 100° C. to about 150° C. to effect a satisfactory cure.

It would be desirable therefore to provide an addition-curable siliconeadhesive composition which could be applied onto an unprimed substrate,such as plastic or metal to effect a satisfactory cure in less than anhour and at a temperature of less than 100° C. In addition, it alsowould be desirable to produce a silicone substrate composite having asilicone layer which would fail cohesively instead of adhesively whentested. As used hereinafter, the expression "adhesive failure" means thesilicone layer can be cleanly separated from the substrate, while in a"cohesive failure", rupture can occur in the silicone layer or in thesubstrate when separation is achieved.

SUMMARY OF THE INVENTION

The present invention is based on the discovery that certainN-heterocyclic silanes, such as bis(trimethoxysilyltrimethylene)2,6pyridine dicarboxylate, have been found to be effective as adhesionpromoters when used in a platinum catalyzed addition-curable siliconecomposition, as defined hereinafter. In addition, the resulting curablecomposition, has been found to provide a silicone adhesive which can becured at temperatures less than 100° C. and in less than 1 hour toproduce a cohesive bond when cured in contact with a plastic or metallicsubstrate.

STATEMENT OF THE INVENTION

There is provided by the present invention, a platinum group metalcatalyzed addition-curable silicone composition, comprising by weight,

(A) 100 parts of a vinyl-containing polydiorganosiloxane compositioncomprising:

(1) about 50 to about 100 parts of an essentially cyclic-freevinyl-terminated polydiorganosiloxane having the general formula,

    (R).sub.2 V.sub.i SiO[(R).sub.2 SiO].sub.m [RV.sub.i SiO].sub.n S.sub.i (R).sub.2 V.sub.i,                                        (1)

where V_(i) is a vinyl radical, R is selected from the class consistingof alkyl radicals having 1 to 8 carbon atoms, phenyl radicals,fluoroalkyl radicals having 3 to 10 carbon atoms and mixtures thereof,"m+n" has a value sufficient to provide a polydiorganosiloxane havingviscosity of 100 to about 100,000 centipoise at 25° C., and a vinylcontent of from about 0.02 to about 2.0 weight %, and

(2) from about 0 to about 50 parts of a solid, benzene-solublevinyl-containing resin copolymer comprising,

    (R.sup.1).sub.3 SiO.sub.1/2 units and SiO.sub.4/2 units,

where R¹ is a vinyl radical, or a monovalent hydrocarbon radical free ofaliphatic unsaturation and containing no more than six carbon atoms, theratio of (R¹)₃ SiO_(1/2) units to SiO_(4/2) units being from about 0.5:1to about 1.5:1, and the vinyl-containing resin having a vinyl content offrom about 1.5 to about 3.5% by weight,

(B) from about 1 to about 20 parts of a hydrogen-containing polysiloxanehaving an average unit formula,

    R.sup.2.sub.a H.sub.b SiO(.sub.4-a-b)/2,                   (2)

where R² is a monovalent hydrocarbon radical, or halogenated monovalenthydrocarbon radical having from 1 to about 10 carbon atoms and free ofaliphatic unsaturation, "a" has a value of from about 0 to about 3, "b"has a value of from about 0 to about 3, and the sum of "a"+"b" has avalue of from 0 to 3,

(C) a catalytic amount of a platinum group metal hydrosilylationcatalyst,

(D) an effective amount of a bis[trialkyloxysilylalkylene]pyridinedicarboxylate adhesion promoter having the formula,

    [(R.sup.3 O).sub.3 S.sub.i R.sup.4 OOC].sub.2 C.sub.5 H.sub.3 N(3)

where R³ is a C.sub.(1-4) alkyl radical and R⁴ is a C.sub.(2-8) alkyleneradical,

(E) from about 0 to about 200 parts of an extending filler, and

(F) from about 0 to about 50 parts of a reinforcing filler, and in theabsence of (A)(2), an amount effective for reinforcement.

In a further aspect of the invention, there is providedbis[trialkyloxysilylalkenyl]pyridine dicarboxylates and method formaking. These compounds can be made by effecting reaction between apyridine dicarboxylic acid halide and an alkenyl alcohol, such as allylalcohol, to form the corresponding pyridine bis alkenyl ester. Atrialkoxysilane, such as trimethoxysilane can be added by use of ahydrosilylation reaction using a platinum catalyst.

The addition-curable compositions of the present invention can be usedas adhesives in industrial multilayered laminates. These adhesives alsocan adhere to substrates that are in contact with the compositionsduring curing. Substrates which are included are glass, metals, metaloxides, and plastics. Among the plastics, there are included,polyetherimides, phenolic resins, epoxy resins, polyamides, unsaturatedpolyesters, poly(ethylene terephthalate), polycarbonates, polyphenylenesulfide, polyacetals, and polyimides.

There are included within the bis[trialkyloxysilylalkyleneoxy]pyridinedicarboxylates of formula (3), referred to hereinafter as the "adhesionpromoters", compounds such as, ##STR1##

An effective amount of the adhesion promoter is 0.3 to 1.5 parts byweight of adhesion promoter, per 100 parts by weight of the platinumgroup metal catalyzed addition-curable adhesion composition, referred tohereinafter as the "addition-curable composition".

The vinyl-terminated polydiorganosiloxane of formula (1) preferably hasa viscosity of from about 3,000 to about 95,000 centipoise at 25° C.Radicals represented by R are preferably alkyl radicals of 1 to about 4carbon atoms, and most preferably methyl.

Component (A) (2) is a vinyl-containing benzene-soluble siloxane resincontaining (R¹)₃ SiO_(1/2) units, or (M units), and SiO_(4/2) units, or(Q units), wherein each R¹ is a vinyl radical, or a monovalenthydrocarbon radical free of aliphatic unsaturation and containing nomore than six carbon atoms, the ratio of (R¹)₃ SiO_(1/2) units toSiO_(4/2) units being from about 0.5:1 to about 1.5:1, the resin havinga vinyl content of from about 1.5 to about 3.5% by weight. Component (A)(2) also is referred to as the "vinyl-containing MQ resin".

Component (A) (2) may further contain (i) R¹ SiO_(3/2) units, (ii) (R¹)₂SiO₁ units, or both (i) and (ii), the (R¹)₂ SiO₁ units being present inan amount equal to from about 0 to about 10 mole percent based on thetotal number of moles of siloxane units in (A) (2), and the R¹ SiO_(3/2)units being present in an amount equal to from about 0 to about 10 molepercent based on the total number of moles of siloxane units in (A) (2).

Component (A) comprises from about 50 to about 100, and preferably fromabout 56 to about 100, and most preferably from about 60 to about 75,parts by weight of (A) (1) and from about 0 to about 50, preferably fromabout 0 to about 40, and most preferably from about 25 to about 40,parts by weight of (A) (2).

In one preferred embodiment of the composition of the present invention,component (A) comprises from about 60 to about 75 parts by weight of (1)a vinyl terminated polydiorganosiloxane having a viscosity of 65,000 toabout 95,000 centipoise at 25° C., and (2) from about 25 to about 40parts by weight of the vinyl-containing MQ resin.

In another preferred embodiment of the composition of the presentinvention, component (A) comprises from about 60 to about 75 parts byweight of (1) a vinyl terminated polydiorganosiloxane having a viscosityof 3000 to about 5000 centipoise at 25° C., and (2) from about 25 toabout 40 parts by weight of the vinyl-containing MQ resin.

In a further preferred embodiment of the composition of the presentinvention, component (A) comprises 100 parts by weight of:

(1) a blend containing from about 25 to about 35 parts by weight of thevinyl-containing polydiorganosiloxane of formula (1) having a viscosityof 3000 to about 5000 centipoise of 25° C. and from about 65 to about 75parts by weight of a vinyl-containing polydiorganosiloxane of formula(1) above and having a viscosity of 75,000 to about 95,000 centipoise at25° C., the total amount of (1) being 100 parts by weight. Preferably,component (A) will additionally contain,

(2) from about 5.5 to about 7.5 parts by weight of a low viscositypolydiorganosiloxane composition having an average of at least onevinyldiorganosiloxy end group, a vinyl content of from about 0.2 toabout 0.3% by weight and a viscosity of from about 400 to about 700centipoise at 25° C.,

(3) from about 5.5 to about 7.5 parts by weight of a low viscosityvinyldiorgano end-stopped, diorganopolysiloxane having a vinyl contentof from about 1.4 to about 2.0% by weight and a viscosity of from about300 to about 600 centipoise at 25° C. and free of the vinyl containingMQ resin. Preferably, reinforcing filler is present in the compositioncontaining (A)-(E), if (A) contains this vinyl polymer blend.

The hydrogen-containing polysiloxane of formula (2) functions as acrosslinking agent. A preferred hydrogen containing polysiloxane has theformula, ##STR2## where R² is as defined above, R⁶ is R² or hydrogen,"c" and "d" have values which are sufficient when added together toprovide a viscosity of from about 10 to about 1000, and as a hydrogencontaining polysiloxane fluid, has a hydrogen content of from about 0.02to about 1.6% by weight.

The hydrogen-containing polysiloxane fluid of formula (4), can be usedas a hydride cross-linking agent in the present invention. In formulas(2) and (4) above, R² is preferably selected from alkyl radicals of 1 to8 carbon atoms, phenyl, fluoroalkyl radicals of 3 to 10 carbon atoms andhydrogen, the preferred fluoroalkyl radical being trifluoropropyl. Mostpreferably, R² represents a methyl radical.

The hydrogen-containing polysiloxane fluid of formula (4) can have aviscosity of from about 10 to about 1000 and preferably from about 10 toabout 150 centipoise at 25° C.

Other hydrogen-containing polysiloxane fluids which can be used in thepresent invention include fluid siloxane copolymer resins comprised of(R¹)₃ SiO_(1/2) ("M") units, SiO_(4/2) ("Q") units, and units such asH(R₂)₂ SiO_(1/2) ("M^(H) "), HR² SiO₁ ("D^(H) ") and (R²)₂ SiO₁ ("D")and mixtures of fluid polyorganosiloxanes and fluid siloxane copolymerresins described in U.S. Pat. No. 3,627,851, which is herebyincorporated by reference herein. The preferred resins are known asM^(H) Q resins, which comprise diorganohydrogensiloxy units (M^(H))units and SiO_(4/2) (Q) units, wherein the ratio ofdiorganohydrogensiloxy units (M^(H)) units to Q units is from 0.4:1.0 to2.0:1.00 inclusive. Hydrogen containing polysiloxanes having at leastone R¹ group, preferably, a methyl group, bonded to silicon which bearsat least one reactive hydrogen atom are preferred. It is to beunderstood that the hydrogen containing polsiloxane can be a singlecompound or a mixture of compounds. Additional hydrogen containingpolysiloxanes suitable for use in the present invention are disclosed,for example, in U.S. Pat. No. 4,061,609 to Bobear, which is herebyincorporated by reference herein.

Further examples of hydrogen-containing polysiloxanes which can be usedin the present invention are linear triorgano endstoppedorganohydrogen-polysiloxane fluids having a viscosity of from about 15to about 40 centistokes at 25° C., and a hydrogen content of 1.6% byweight. These hydrogen containing polysiloxanes generally have theformula,

    (R.sup.2).sub.3 SiO(HR.sup.2 SiO).sub.e Si(R.sup.2).sub.3, (5)

where R² is as previously defined herein and "e" is a number sufficientto provide a viscosity of from about 15 to about 40 centistokes at 25°C.

It is preferred that the hydrogen-containing polysiloxane of formulas(4) and (5) have a hydride content of 0.05 to 1.6%, and more preferablyof 0.1 to 1% by weight. In instances where the vinyl containingpolydiorganopolysiloxane of formula (1) has a viscosity of between 3000to 5000 centipoise and the hydrogen containing polysiloxane is atriorgano end-stopped organohydrogensiloxane, the SiH:SiVinyl ratio ispreferably at least 2.1:1, while about 2.1:1 to about 10.1, or fromabout 2.1:1 to about 3.5:1 is particularly preferred.

Component (C) of the adhesion composition of the present invention whichpromotes the hydrosilylation reaction is a platinum group metalcatalyst. Additional catalysts for facilitating the hydrosilylationcuring reaction include precious metal catalysts such as those which useruthenium, rhodium, palladium, osmium, and iridium, and complexes ofthese metals. Examples of suitable hydrosilylation catalysts for use inthe present invention are disclosed, for example in U.S. Pat. Nos.3,159,601 and 3,159,662 (Ashby); 3,220,970 (Lamoreaux); 3,775,452(Karstedt), 3,516,946 (Modic), and 4,029,629 (Jeram); all of theforegoing patents being hereby incorporated by reference herein.

Preferable, the hydrosilylation catalyst is a platinum containingcatalyst. A preferred platinum-containing catalyst is a platinum-octanolcomplex containing 90.9 weight % octyl alcohol and 9.1 weight %chloroplatinic acid.

Another preferred platinum-containing catalyst is a platinum complexformed by reacting chloroplatinic acid containing 4 moles of water ofhydration with tetravinylcyclotetrasiloxane in the presence of sodiumbicarbonate in an ethanol solution. This catalyst is disclosed in U.S.Pat. No. 3,775,452 to Karstedt, which is hereby incorporated byreference herein.

The catalyst must be used in a catalytic amount, which is that amountsufficient to promote the hydrosilylation reaction. Generally, theremust be utilized at least 0.1 part per million of a platinum catalyst,and preferably from 5 ppm to 250 ppm, in terms of parts of platinummetal based on the weight of hydrosilylation mixture. Inhibitors, suchas acetylenic alcohols, amines, and cyanurates also can be employed whenused in an effective amount.

The composition of the present invention may also contain any of theconventional (E) extending and/or (F) reinforcing fillers. Thecomposition contains from about 0 to about 200 and preferably from about10 to about 100 parts by weight of (E) an extending filler, and fromabout 0 to about 50, and preferably from about 20 to about 50 parts byweight of (F) a reinforcing filler.

Examples of extending fillers (E) useful herein include alpha quartz,crushed quartz, aluminum oxide, aluminum silicate, zirconium silicate,magnesium oxide, zinc oxide, talc, diatomaceous earth, iron oxide,calcium carbonate, clay, titania, zirconia, mica, glass, such as groundglass or glass fiber, sand, carbon black, graphite barium sulfate, zincsulfate, wood flour, cork, fluorocarbon polymer powder and the like. Thepreferred extending filler for use in the present invention is alphaquartz.

Examples of reinforcing fillers (F) include silica, such as fumed silicaand precipitated silica, and treated silica fillers such as fumed orprecipitated silica that has been reacted with, e.g., anorganohalosilane, a disiloxane, or a disilazane. Fumed silica isparticularly effective as a reinforcing filler for the siliconecomponent of the present invention. A particularly preferred treatedfumed silica is one wherein a fumed silica has been treated first withcyclic polysiloxanes, e.g., dimethylcyclic tetramer, according to themethods known in the art, for example, as taught in U.S. Pat. No.2,938,009 (Lucas), which is incorporated by reference herein, and thentreated with a silazane, e.g., hexamethyldisilazane, for example, astaught in U.S. Pat. Nos. 3,635,743 (Smith) and 3,847,848 (Beers), whichare both incorporated by reference herein, so as to remove most of thefree silanols on the surface of the tetramer treated silica. Such afiller is sometimes referred to herein as "treated fumed silica".

The composition of the present invention can be prepared byhomogeneously mixing components (A)-(F) and any optional ingredients,using suitable mixing means, such as a spatula, a drum roller, amechanical stirrer, a three-roll mill, a sigma blade mixer, a breaddough mixer and a two-roll mill.

The order of mixing components (A)-(F) is not critical, however, it ispreferred that components (B) and (C) be brought together in thepresence of component (D), most preferable in a final mixing step. Thus,it is possible to mix all components in one mixing step immediatelyprior to the intended use of the curable composition. Alternatively,certain components can be premixed to form two or more packages whichcan be stored, if desired, and then mixed in a final step immediatelyprior to the intended use thereof.

It is preferred to mix components (C), (D), and a portion of component(A), along with certain optional components, such as fillers andsolvents, to provide a first package. Separately, component (B), alongwith the remaining portion of component (A), if any, can be mixed toprovide a second package. These two packages can then be stored untilthe composition of this invention is desired and then homogeneouslymixed.

The addition-curable silicone compositions of the invention willdirectly self-bond in the absence of primer to various plastic, metal,glass, and masonry substrates. Examples of metal substrates includemetal substrates selected from copper, alclad aluminum, anodizedaluminum, galvanized steel, cold-rolled steel, cast aluminum, and castmagnesium. In particular instances it is preferred to "condition"certain substrates such as polyetherimide by treating the polyetherimidesubstrate with a 5M KOH solution at 70° C. for 5 minutes followed by arinse. The thickness of the adhesive composition on a substrate istypically from about 20 to about 60 mils.

The addition-curable compositions of the present invention can beapplied onto the surface of the substrate by any suitable means such asrolling, spreading, spraying, and the like, and cured as describedabove. After application of the adhesive composition onto the substrate,the composition can be cured at a temperature in the range of about 50°C. to 100° C. over a period of about 10 to 30 minutes.

In order that those skilled in the art may better understand thepractice of the present invention, the following example is given by wayof illustration and not by way of limitation. All parts are by weight.

EXAMPLE 1

A mixture of 5 g of 2,6 pyridine dicarboxylic acid and 25 ml of thionylchloride was heated under reflux conditions until the mixture becamehomogeneous. Excess thionyl chloride was removed in vacuo. There wasobtained 6.0 g of product. Based on ¹ H NMR the product was thecorresponding pyridine bis acid chloride.

A mixture of 20 g of allyl alcohol and 6 g of the bis acid chloride wasrefluxed to provide 7 g of the diallyl pyridine dicarboxylate.

There was added dropwise via a syringe, 10 ml of trimethoxysilane to amixture under nitrogen of 7 g of diallyl 2,6 pyridine dicarboxylate and10 μL of a platinum-vinylsiloxane complex shown in Karstedt U.S. Pat.No. 3,775,452. The mixture was heated to 80° C. for 1 hour. Excesstrimethoxysilane was removed in vacuo. There was obtained about 7 g ofproduct. Based on ¹ H NMR, the product was bis(trimethoxysilylpropenyl)2,6 pyridine dicarboxylate referred to below as the adhesion promoter.

A heat addition-curable silicone formulation was prepared by adding 0.23g of a methylhydrogensiloxydimethylsiloxy copolymer having a hydrogencontent of about 0.8% by weight to a mixture of 13 g of mixture of apolydimethylsiloxane having terminal dimethylvinylsiloxy units and aviscosity of about 40,000 centipoise and 20% by weight of the mixture offumed silica treated with octamethylcyclotetrasiloxane, 10 ppm ofplatinum in the form of a solution of platinum catalyst shown inKarstedt U.S. Pat. No. 3,775,452, 3 μL of 3,5 dimethyl-1-hexyn-3-ol and0.04 g the above adhesion promoter.

Several 1"×1/2" coupons of aluminum, were cleaned using an Oakite®detergent wash at 60° C., or an isopropanol wipe. Similar size testsamples of Ultem® polyetherimide of GE Plastics Div. were also preparedby immersion in 5M KOH at 70° C., followed by a distilled water rinse.

Al/Al and polyetherimide lap shear test samples were prepared which wereheated at 80° C. for 15 minutes. There were obtained composites whichfailed cohesively after a >200 psi shear test for the aluminumcomposites and a 400 psi shear test for the polyetherimide composites.All the composites were found to fail adhesively when the adhesionpromoter was omitted after being cured under the same conditions.

Although the above example is directed to only a few of the very manyvariables which can be used in the practice of the present invention, itshould be understood that the present invention is directed to a muchbroader variety of bis(trialkoxysilylalkenyl) 2,6 pyridine dicarboxylateadhesion promoters and addition-curable organopolysiloxane compositionscontaining such adhesion promoters as shown in the description precedingthese examples.

What is claimed is:
 1. An addition-curable composition, comprising by weight,(A) 100 parts of a vinyl-containing polydiorganosiloxane composition comprising:(1) about 50 to about 100 parts of an essentially cyclic-free vinyl-terminated polydiorganosiloxane having the general formula,

    (R).sub.2 V.sub.i SiO[(R).sub.2 SiO].sub.m [RV.sub.i SiO].sub.n S.sub.i (R).sub.2 V.sub.i,

where Vi is a vinyl radical, R is selected from the class consisting of alkyl radicals having 1 to 8 carbon atoms, phenyl radicals, fluoroalkyl radicals having 3 to 10 carbon atoms and mixtures thereof, "m+n" has a value sufficient to provide a polydiorganosiloxane viscosity of 100 to about 100,000 centipoise at 25° C. and a polydiorganosiloxane vinyl content of from about 0.02 to about 2.0 weight %, and (2) from about 0 to about 50 parts of a solid, benzene-soluble vinyl-containing resin copolymer comprising,

    (R.sup.1).sub.3 SiO.sub.1/2 units and SiO.sub.4/2 units,

where R¹ is a vinyl radical, or a monovalent hydrocarbon radical free of aliphatic unsaturation and containing no more than six carbon atoms, the ratio of (R¹)₃ SiO_(1/2) units to SiO_(4/2) units being from about 0.5:1 to about 1.5:1, and the resin having a vinyl content of from about 1.5 to about 3.5% by weight, (B) from about 1 to about 20 parts of a hydrogen-containing polysiloxane having an average unit formula,

    R.sup.2.sub.a H.sub.b SiO.sub.(4-a-b)/2,

where R² is a monovalent hydrocarbon radical, or halogenated monovalent hydrocarbon radical having from 1 to about 10 carbon atoms and free of aliphatic unsaturation, "a" has a value of from about 0 to about 3, "b" has a value of from about 0 to about 3, and the sum of "a"+"b" has a value of from 0 to 3, (C) a catalytic amount of a hydrosilylation catalyst, (D) an amount of a bis[trialkyloxysilylalkenyl]pyridine dicarboxylate having the formula,

    [(R.sup.3 O).sub.3 S.sub.i R.sup.4 OOC].sub.2 C.sub.5 H.sub.3 N

which is effective as an adhesion promoter, wherein R³ is a C.sub.(1-4) alkyl radical and R⁴ is a C.sub.(2-8) alkylene radical, (E) from about 0 to about 200 parts of an extending filler, and (F) from about 0 to about 50 parts of a reinforcing filler, and in the absence of (A)(2), an amount effective for reinforcement.
 2. An addition-curable composition in accordance with claim 1, where the vinyl-containing polydiorganopolysiloxane is a vinyl-containing polydimethylsiloxane.
 3. An addition-curable composition in accordance with claim 1, where the solid, benzene-soluble vinyl-containing resin comprises a mixture of (CH₃)₃ SiO_(1/2) units and Vi(CH₃)₂ SiO_(1/2) units and SiO₂ units.
 4. An addition-curable composition in accordance with claim 1, where the hydrosilylation catalyst is a platinum catalyst.
 5. An addition-curable composition in accordance with claim 1, where the adhesion promoter is 2,6 bis(trimethoxysilyltrimethylene)pyridine dicarboxylate. 